The overall goal of the Tetramer Core is to develop and provide HLA Class I/peptide tetramers for use by Program Project Investigators in Projects 1, 2, 3 that examine the induction and maintenance of virus- specific CD8+ T cell-mediated immunity in humans across the age spectrum. Recently, the laboratories of Davis and McMichael have pioneered technological advances that allow the direct detection, quantitation, and isolation of antigen-specific T cells in the peripheral blood by using a fluorescent-labeled tetrameric complex of components consisting of MHC Class I alpha chain, beta2-microgolubin, and an antigenic peptide (HLA Class I/Peptide Tetramers). Individual HLA Class I-peptide tetramers must be generated for each antigen peptide to be studied at present, the availability of HLA Class I-peptide tetramers is extremely limited We therefore propose to apply or experience in the construction of the HLA Class I/HIV-1 peptidramers to the construction of tetramers for use by Program Project investigators in their studies of virus-specific CD8+ T cell immunity in human viral infections. Tetramer Core personnel will be responsible for the generation and distribution of tetramers. The generation of tetramers for Program Project Investigators will be prioritized based on identified epitopes and the distribution of HLA Class I alleles in the populations under study. The availability of this new technology to Program Project investigators should greatly enhance their ability to enumerate, isolate, and characterize virus-specific CD8+ T cells in human viral infections.